LAUSR

OBJECTIVE To establish and compare the onset and duration of action of 2 local anesthetics based on objective lameness and skin sensitivity assessment. STUDY DESIGN Interventional crossover experimental trial with balanced randomization. ANIMALS Eight horses. METHODS Reversible forelimb lameness was induced in 8 horses. A palmar digital nerve block (PDNB) was applied with mepivacaine or lidocaine (both 2%). Quantitative lameness and skin sensitivity data were collected with an inertial sensor system and a force gauge, respectively. The times to lameness resolution/skin desensitization (T1), consistent lameness detection/partial return of skin sensitivity (T2), and complete return of lameness/skin sensitivity (T3) were determined and compared between treatments and assessment methods. RESULTS Mepivacaine blocks resolved lameness in 8/8 horses, compared to 3/8 horses with lidocaine blocks. Both agents led to skin desensitization in 8/8 horses. Skin desensitization occurred sooner than lameness resolution after mepivacaine (P = .047). Duration of action was longer with mepivacaine than lidocaine (mean T3_lameness mepivacaine 366 minutes, lidocaine 113 minutes (P = .038); T3_skin mepivacaine 195 minutes, lidocaine 63 minutes [P ≤ .001]). Skin sensitivity returned sooner than lameness after lidocaine block at T3 (P = .015). CONCLUSION The use of lidocaine in PDNBs for the purpose of lameness diagnosis should be reassessed, as it may not resolve lameness despite loss of skin sensation. Mepivacaine is superior, with a reliable onset and longer duration of action. Skin desensitization as an indicator for the onset of action or effectiveness of PDNBs for mepivacaine and lidocaine, or as a measure of the duration of action of lidocaine PDNBs should be interpreted with caution.